Visit Zoo to see Amazon's Largest Fish

The zoo’s aquarium is the home for large fish. Among them, you’d find one of the world’s largest freshwater fish, a habitant of the Amazon River - arapaima. They are true giants and ZooLander recommends that you closely observe these large fish.

At a quiet corner of the aquarium is a large tank. In it swims a group of large fish. They are well near 5 or 6 feet long, and are surely the heaviest fish in the aquarium. Everybody wants to have a peek at these monster fish, but the little known fact is that they are in fact one of the world’s largest freshwater fish.

Named arapaima, these fish are inhabitants of the biodiversity rich Amazon River. In local Amazonian languages, this giant fish  is also called pirarucu or paiche. Because of their enormous size, this giant is also mentioned in the legends of the local Amazonian tribes. According to legend, Pirarucu is the disrespectful and cruel son of an Amazon chief. God has struck him down to the depths of the river, and it became the arapaima. Brazilians and locals still refer to the fish as pirarucu.

Whatever the legend holds, the monster fish is also referred to as a living fossil by historians. They believe these fish have inhabited these Amazonian regions since the Jurassic age, millions of years back. The fossil records too supports this theory making the arapaima a living fossil fish and a true prehistoric river monster. In other words theyt could have been there during the same time as dinosaurs and can truly be called Dino-fish from the deep.

They are truly giants in freshwater, and records indicate that fish as long as 9 feet are caught from the Amazon River. An unconfirmed record from  the 19th century also reports of fishermen having caught an arapaima the length 14.8 ft (4.5m). A full grown arapaima can weigh as heavy as 440 pounds (200 kilograms). Arapaima has a wide, scaly, grey body and a tapered head. This gives them somewhat of a bizarre look and establishes their name as a monster river fish. This dino fish is indeed a predator of the deep. Usually they hunt other fish, crustaceans and other small animals. It is also claimed that the arapaima sometimes feed on water birds that are low flying or swimming without a sense of the lurking dangers that lie beneath.

Most of the fish breathe through their gills, and can stay underwater without a problem. But the arapaima is strangely an air breather, getting oxygen from air inhaled through the mouth. Arapaimas can stay underwater for 10 to 20 minutes, and tend to remain near the water’s surface, where they hunt and emerge often to breathe with a distinctive coughing noise, say experts.

Labyrinth organ

They have a special organ - the  labyrinth organ which is rich in blood vessels that opens into the fish’s mouth. This also helps the arapaima to survive in waters where the oxygen level is low.  Lakes in the Amazon region which are are isolated from other rivers during the dry season brings down the oxygen levels but this giant fish survives as it has the advantage of the ability to breathe air.

However, this air breathing habit also results in the arapaimas’ downfall. Because they have to surface to breathe, they are easy targets of fishermen, and others who hunt them for fun. Arapaimas are caught using nets or by harpooning. Once an Arapaima is detected, the fishermen can be certain that it could emerge somewhere near and stay ready to harpoon it. This has caused the  decline of the fish population pushing it to Vulnerable and to  Extinction status in the IUCN Red List of Threatened Species. Because the arapaima can be cooked in to “large, boneless fish steaks” it is considered a delicacy, and records show some 7000 tons per year were fished from 1918 to 1924, at the height of it being commercialycaught. But recognizing the threat, the commercial fishing of arapaima has now been banned in the Amazon region. Fishing is allowed only in certain remote areas and on a catch-and-release, basis or harvesting by native people for their consumption. Raising arapaimas for food is allowed.

The reproduction cycle of this giant fish is also interesting. They build a nest at the bottom of rivers where it is muddy. Experts say that the nest is about 50cm wide and 15cm deep. It is said that the arapaima breeds in drier periods where water levels are low or at times when water levels just start to rise. As the water rises the eggs hatch and the offspring have the flood season to prosper, during the months from May to August. Because of this, the yearly  spawning is regulated seasonally in this region.

The father arapaima is truly the most dedicated of parents. “Mouth incubation” is thought to take place. Arapaimas are mouthbrooders with the eggs and young  protected in the mouth. This task is done by the father, who takes on the duty of protecting the babies. The father guarding the eggs is known to take the young and egss in his mouth and move them to another location. The young are led by the male in a group, once they are able to swim. The mother gives protection to the father by staying and swimming close, ready to interfere in case of an attack. This is truly the gentle side of this giant fish.

published on LakbimaNews on 05.02.2012 http://www.lakbimanews.lk/index.php?option=com_content&view=article&id=4412:visit-amazons-dont-dine-on-the-dino&catid=41:mag&Itemid=12